“With the latest major release of the Android OS, codenamed “Lollipop”, Google is playing its best cards to enter the enterprise market. Android 5.0 Lollipop has introduced new features, security enhancement and upgraded API for device management; it can now be considered a mature operating system to be used in critical environment and a potential major player in the enterprise world. The talk will explore new features such as the “kill switch” factory reset, the smart lock functionality and other innovative security features and improvements. The session will end with a deep technical discussion on the device management extensions offered by Android; it will focus on the new “managed profile” feature for “containerization technology”, based on the integration of Samsung‘s KNOX platform, which offers the ability to run enterprise applications in a secure protected environment and to keep the working and personal spaces independent from each other.”

Technical details and code examples will be demonstrated during the presentation.

Thanks to the DeepSec team, the presentation of mseclab team “Hijacking Mobile Data Connections 2.0: Automated and Improved”, held in November 2009 in Vienna, has been published at vimeo website.

This presentation explains some techniques, effective still today, to hijack device originated Mobile Data Connections, on any phone equipped with OMA client. Furthermore, automated technique is shown to retrieve victim’s IMSI in order to select the right APN Mobile Operator Configuration; how to perform an SSLSTRIP attack has also been demonstrated.

SSL is the de-facto standard for securing communications between a user and a server against third parties. If someone is able to intercept, hijack, or have access in any other way to our network traffic, SSL provides an effective line of defense against eavesdropping.

Basically, all the devices have to do is check that the certificate protecting the connection to site “foo” carries a label (the CommonName Field) stating it belongs to site “foo”, and warn the user if it does not, something that is actually more complicated than it seems. At Black Hat USA 09, during the talk “More Tricks for Defeating SSL” given by Moxie Marlinspike, the “Null Prefix” attack was presented; the security researcher leveraged the fact that the string containing the domain name is represented using ASN.1 encoding as:

[domain_name length] domain_name

while many programs (browers, mail clients, and those used internally by CA’s) use the ‘C’ standard (null terminated-string) instead:

domain_name[\0]

So he generated Certificate Requests for domain names containing a null character (\0 or \x00), for example “paypal.com\0.thoughtcrime.org”, and managed to get them signed by an official Certification Authority; several CAs verified that the request came from “thoughtcrime.org”, while the applications thought the certificate belonged to paypal.com.

The researcher discovered that the applications built with Mozilla NSS Library ( Network Security Services that support SSL/TLS standards) are vulnerable to wildcard certificates generated in the same way. From a certificate request for *\0.thoughtcrime.org, it is possible to obtain a certificate valid for every domain!

Another attack variation consists of generating a certificate for “sitekey.ba\0nkofamerica.com”: the sitekey.ba domain is used for requesting validation but the resulting certificate is valid for the domain “sitekey.bankofamerica.com” for SSL implementations that simply strip the “\0” character.

The attack was fundamentally meant for desktop environments; we immediately wondered how it applies to mobile environments; so we’ve spent some time to test the attacks against some mobile devices. We’ve reported the results of our tests in the following table:

During the same days of our Hijacking attack presentation at BH EU ’09, we read of “a-sort-of” SMS hijacking attack performed on Windows Mobile phones. On the demonstrating video here a binary SMS is sent to a Windows mobile phone, and the browser suddenly pops up, opening an attacker specified URL. That’s the typical behaviour of an handset receiving a Service Load (SL) message, and actually this type of attack had already been discussed (here and here). We feel that this might still be a somewhat underestimated risk in the mobile environment, as Service Loading is supported by many platforms apart from Windows Mobile; but before going deeper into that, let’s explain what Service Loading messages are and what are they for.

Service Loading is a part of the WAP Push protocol suite for OTA (Over The Air) provisioning of mobile handset. It is often cited together with Service Indication: like Service Loading, Service Indication is used to carry URL addresses to the handset in a binary SMS message; but it is rather meant to notify the user of a certain URL in order to be, for instance, added to the bookmarks, and not necessarily to open it at once.

Let’s see the basic structure of a SL message:

As any other WAP protocol element, it uses an XML representation; the actual SL element have only two attributes: an URI (commonly said to be URL) and an action; the latter can be “execute-high”, meaning the content is executed in an user-obtrusive (visible) manner, “execute-low”, meaning the content is executed in a non user-obtrusive (invisible) manner, and “cache”, meaning that the content should simply be put in browser’s cache, not executed neither displayed. The default is execute-low. In order to be sent, this document must be converted to WBXML format (a compressed binary representation), then stuffed in an SMS message according to WSP protocol.

Upon receiving such a message, if the URI is an HTML page, the phone will load and show it with the default web browser; if it is an executable program, it will download and execute it, possibly in a silent way. The risk associated with this feature, especially without user’s awareness, should be obvious also for non tech savvy readers; that’s why most handsets come with some sort of security policy associated with WAP Push messages.

We have conducted a test on two largely used devices, a Nokia N95 and a Sony Ericsson C905, to check how they deal with Service Loading messages.

We hadn’t the chance to be at BH USA ’09, but we’ve seen there have been several talks about mobile security; and there seems to be a solid consensus in considering this as the new frontier of security. Mobile devices nowadays support many complex interfaces and protocols: GSM/UMTS network, IP network, Bluetooth, Smart cards…; this doesn’t only mean exposing more surface to attacks than traditional computers, but also that the mix of several small, unrelated security flaws could result in a much bigger one.Black Hat USA 09 archives list a speech by Jesse Burns, of ISEC Partners, about Android’s security model, while Kevin Mahaffey, John Hering and Anthony Lineberry of Flexillis presented a non device-specific fuzzer for mobile platforms.
But the most impressive work was presented by Charlie Miller and Colin Mulliner; they managed to inject SMS messages past the radio section directly into phone’s processing chain. This technique has been applied to iPhone, Android and Windows Mobile; not having to rely on the network to send messages gets rid of the associated costs, and allows for a fast and thorough test (fuzzing) of SMS processing stack. The results were up to the expectations: actually, both Android and iPhone could be crashed by malformed binary messages, allowing for effective Denial of Service attack, while Windows Mobile is still under scrutiny. The vulnerability on iPhone was also found to potentially allow for remote code execution with full privileges, without any user advice nor any way to stop messages.
While Apple had to quickly release a security update, SMS is confirmed as one of the most investigated attack vectors.
However, other general issues could have a significant impact on mobile security; Moxie Marlinspike’s “More Tricks for Defeating SSL” is an effective attack against (almost any) popular web browsers, but it affects connections from mobile devices as well. As we pointed out, SSL is the last line of defense against the “Hijacking mobile data connection” attack we discovered, so knowing it can be attacked isn’t reassuring at all. We’ve began testing the attack on various mobile platforms, and we will post the result as soon as we can.

In the last days, there has been lots of talking about weak security of Google ‘cloud’ services: after the authentication on encrypted protocol (HTTPS), all data exchange between user and Google servers takes place on plain HTTP, thus allowing for easy attack or eavesdropping. Wired reports that, for this reason, several security experts signed a public petition to ask Google to protect complete user sessions with SSL. From our mobile enviroment perspective, we cannot but to completely agree.

The abusing of the OMA provisioning mechanism, supported by a great extent of modern mobile devices, as we pointed out, demonstrates beyond any doubt how concrete the risk is. Ironically, while provisioning protocol makes abusing mobile devices configuration so easy, many sites do use secure (SSL) protocols, but not when accessed by mobile devices; probably because, given their reduced computational power, these are considered unfit to cope with encryption in an effective way.

Continuing our exploration of what the consequences of Data Session Hijacking could be, we went a step further. In Proxy Fun we reported that hijacking by means of remote proxy configuration only affects HTTP traffic (and HTTPS as well), that could be considered as a limitation but, by contrast, allows for some HTTP-specific hijacking techniques more easily than a remote DNS configuration.
Actually, the original attack we presented at BH Europe 2009, based on DNS configuration, was still unable to intercept and handle HTTPS connections, thus still being ineffective with sites that used this protocol for authentication.
Proxy configuration makes hijacking effective on a new mobile site category: those (email providers, social network, e-commerce) that use HTTPS protocol for logging in, and then switch to HTTP protocol for the rest of the session. Exactly like Google – that, by the way, is still more secure than several services that make no use of SSL whatsoever; we have found several ones.

So, hijacking by means of a proxy configuration means passing HTTPS authentication without interception by CONNECT method, then getting the session cookie (called GX for Gmail) from subsequent HTTP requests and using it to hijack the user session – a technique called “sidejacking”. You don’t have to think that only exchanged data is at risk; the attacker gets authenticated to the server and can operate on the server as if he was the user. An attacker, for example, could write, send and delete mails on behalf of the victim user or delete the user’s documents.

Sidejacking, or using the victim session cookies to impersonate him, was demonstrated by the founders of Errata Security at BlackHat Usa 2007. Also an evolution of this technique has been proposed, called forced sidejacking, that makes use of ‘HTTP 302 Temporarily moved’ web pages for collecting victim cookies.

In the following video we show how remotely configuring an LG KM900, in order to force it to go through an evil proxy server, looks like; then the attacker easily grabs the GX cookie released within a Gmail mobile session and uses it in his browser to hijack the mobile session.

In the previous post Hijacking Mobile Data Connections , we pointed out how an attacker could gain full control on mobile data connections originated by mobile phone.

This could be achieved by reconfiguring the DNS address on victim’s mobile phone with one controlled by the attacker, by means of OMA provisioning SMS. However, during our tests some mobile phones resisted to this attack, due to the fact that, despite supporting OMA provisioning, they don’t honour configuration requests of DNS address, neither locally nor remotely.

But, as we said, OMA provisioning allows for setting other parameters than DNS; among them there are the proxy settings.

In mobile world, a proxy isn’t different from any other environment: it is a software component that is located between a client, in this case a mobile phone, and a server on Internet; any standard HTTP proxy can be used for an HTTP mobile client.

In our experiences we have noticed that the proxy settings are widely used by several operator services, mainly for delivering MMS messages.

On the other side, an attacker could use proxy configuration to hijack the victim traffic, HTTP and HTTPS, and redirect it towards an IP address under his control. Still the victim, after having installed the rogue configuration, will be unaware that a third party, the attacker, is eavesdropping the data traffic.

Hijacking by means of a proxy configuration has some differences with respect to DNS configuration, apart from being supported by a few more phones:

Proxy component is enough to redirect user’s data traffic.

The proxy port could be set to a different value, other than the standard TCP/80. This could be useful for the attacker to overcome some firewall restriction.

While the operator could block DNS traffic to outside of its network, in order to mitigate attacks to DNS settings, it may be difficult to restrict access to HTTP proxies over Internet;

The limitation, of course, is that only HTTP-based services could be hijacked; this excludes email and most dedicated clients.

Here we are with another sample of our attack technique described in the “Hijacking Mobile Data Connections” post. Today we are going to show you how the attack can have a significantly deeper impact depending on the design of the target handset: specifically, some defects in the provisioning messages processing code, together with a less than optimal User Interface design, lead to a significant advantage for an attacker trying to compromise the device.
In this case no ‘social engineering’ or spoofed messages are required.

As described in our MSL-2009-001 advisory (“Samsung Missing Provisioning Authentication”), we have identified some handsets that don’t perform proper authentication of incoming SMS Provisioning messages. They never display the source of the message; moreover, and much more worrying, they accept both authenticated and unauthenticated provisioning messages without giving to the user any hint of the nature of the message itself. To install the configuration inside it, user simply has to open the incoming message, while no authentication is in effect.

The following video shows how the attack is performed against these devices.

It is important to highlight that both unauthenticated messages and authenticated ones (whether by USERPIN or NETWORKPIN mechanism) are presented to the user in exactly the same way.
This has a deep impact on the security level perceived by the user: a competent one, in fact, could base its judgement of the message authenticity on the fact that it is authenticated by a specific mechanism. In order to produce a correct NETWORKPIN-authenticated message, the sending party has to know the IMSI of the victim, which is usually considered a private information, known only to the user itself and to the operator he belongs to.
The user, seeing that he is not asked to input any PIN, is led to think that the provisioning message is of the NETWORKPIN-authenticated type, and that, being so, it has to come from the operator’s systems; this reinforce, in the user, the belief that he can safely accept the new configuration.

MSL-2008-001 vulnerability raised a significant attention; we have now decided to disclose its technical details. We decided to proceed with the disclosure in order to stimulate public analysis and contribution, hoping to increase awareness about this issue and ultimately help protection against it.

The following description is based on our tests and our inference of what happens inside the device.
Unfortunately, researching vulnerabilities on such devices is a long and painful work, because of the lack of documentation, testing tools and debuggers, so we cannot ultimately state what happens at the code level.

All evidences are towards a vulnerability occurring in the parsing of WAP Push header; the code devoted to such parsing appears to be used for processing packets received both on SMS and IP.

We strongly believe that the specific issue resides in the improper handling of incorrect size fields inside the WAP Push headers.

WAP is actually a large framework, into which WSP is in charge of content delivery. A reference document describing WSP protocol can be found here:

WSP makes extensive use of size fields; our tests have tracked a few fields that, if incorrectly specified, will lead the vulnerable handsets to an error condition, such as rebooting or system freezing. More specifically, the vulnerability will be triggered if, in such fields, the specified length is larger than the actual amount of bytes.

Since WAP content can be carried both over SMS and IP protocol, we will make use of the latter to show an example; this enables us to use Wireshark to better explain the data structures.

The following pictures show the capture of 2 sample IP packets that, when sent to the handset, will make it reboot; they have been opened with Wireshark, even though they are marked (obviously) as ‘malformed’.
The lower pane shows the hexadecimal representation of WAP payload.

Fig 1 – MSL-2008-001-1

Figure 1 shows one of the first formats we researched: this is a WAP Push message carrying a “multipart” Content-Type payload. According to the specifications, the 2 bytes circled in the screenshot refer to the multipart payload headers:Header Length: 0x0a
Content Length: 0x1

In the remaining part of the packet there are only 0xa bytes, and no byte is referenced by the 0x1 of the Content Length. This is enough for triggering the vulnerability; changing the Content Length to 0x0 would fix the header and the payload would be normally processed by the handset without any consequence.

Let’s see another example:

Fig 2 – MSL-2008-001-2

This sample does not use any multipart content, it just consists of the WAP Push packet header, without any payload. The specified Header Length (3rd byte) is 0x1c bytes long, while there
are just 0x1b remaining bytes in the header. Changing the Header-Length to the correct value of 0x1b would fix the header resulting in an inoffensive WAP Push packet.

These malformed WAP Push packets are to be sent over UDP, but the very same payload can be embedded in a properly formatted SMS.

We are not sure that all the possible attack vectors have been identified; and the two samples, even if they yield the same effect, may actually be due to different code execution flows.

Besides, it seems that the vulnerability occurs quite early in the processing of the WAP packet, because the UI settings are not able to influence in any way the processing of such packets.
The vulnerability occurs long before anything is displayed on the UI, and the received SMS is not even saved in the Inbox.

The ‘closed’ OS and the characteristics of this vulnerability suggest us that a protection on the network side could be a viable alternative to that on the handset side, but other options may apply too.